Semiconductor light emitting devices such as light emitting diodes (LEDs) are among the most efficient light sources currently available. Material systems currently of interest in the manufacture of high brightness LEDs capable of operation across the visible spectrum include group III-V semiconductors, particularly binary, ternary, and quaternary alloys of gallium, aluminum, indium, and nitrogen, also referred to as III-nitride materials; and binary, ternary, and quaternary alloys of gallium, aluminum, indium, arsenic, and phosphorus. Often III-nitride devices are epitaxially grown on sapphire, silicon carbide, or III-nitride substrates and III-phosphide devices are epitaxially grown on gallium arsenide by metal organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), or other epitaxial techniques. Often, an n-type region is deposited on the substrate, then a light emitting or active region is deposited on the n-type region, then a p-type region is deposited on the active region. The order of the layers may be reversed such that the p-type region is adjacent to the substrate.
One promising use of semiconductor light emitting devices is for backlights in liquid crystal displays (LCDs). LCDs are commonly used in cellular phones, personal digital assistants (PDAs), portable music players, laptop computers, desktop monitors, and television applications. One embodiment of the present invention deals with a color or monochrome, transmissive LCD that requires backlighting, where the backlight may use one or more LEDs emitting white or colored light. Embodiments using blue LEDs and a remote phosphor layer for white light generation are also possible. The LEDs are distinguished from laser diodes in that the LEDs emit incoherent light.
One backlight is described in US Published Application 2009-0045420, which is incorporated herein by reference, and illustrated in FIG. 1. “A side-emitting LED 10, mounted on a mount 22, is positioned in an opening in a section of solid, transparent waveguide material 36 . . . . Waveguide section 36 [is] positioned in slot 42 of a larger waveguide 40.”